Fixed-bearing knee prosthesis having interchangeable components

ABSTRACT

A fixed-bearing prosthesis includes a femoral component having a medial condyle surface and a lateral condyle surface. The knee prosthesis also includes a bearing having a medial bearing surface configured to articulate with the medial condyle surface of the femoral component, and a lateral bearing surface configured to articulate with the lateral condyle surface of the femoral component. A tibial tray is secured to the bearing. The tibial tray has a platform with an elongated stem extending downwardly from a lower surface thereof. A posterior buttress extends along a posterior section of the perimeter of the tray&#39;s platform, and an anterior buttress extends along an anterior section of the perimeter of the tray&#39;s platform. Differently-sized tibial trays are interchangeable with differently-sized bearings.

This application is a continuation of copending U.S. patent applicationSer. No. 12/904,614 filed Oct. 14, 2010, which is a continuation-in-partof U.S. Pat. No. 8,128,703 filed on Nov. 17, 2009, which is acontinuation-in-part of U.S. Pat. No. 7,628,818 filed on Sep. 28, 2007.The entirety of each of those applications is expressly incorporatedherein by reference.

TECHNICAL FIELD

The present disclosure relates generally to an implantable orthopaedicprosthesis, and more particularly to an implantable knee prosthesis.

BACKGROUND

During the lifetime of a patient, it may be necessary to perform a jointreplacement procedure on the patient as a result of, for example,disease or trauma. The joint replacement procedure may involve the useof a prosthesis which is implanted into one or more of the patient'sbones. In the case of a knee replacement procedure, a tibial tray isimplanted into the patient's tibia. A bearing is secured to the tibialtray. The condyle surfaces of a replacement femoral component bearagainst the tibial bearing.

One type of knee prosthesis is a fixed-bearing knee prosthesis. As itsname suggests, the bearing of a fixed-bearing knee prosthesis does notmove relative to the tibial tray. Fixed-bearing designs are commonlyused when the condition of the patient's soft tissue (i.e., kneeligaments) does not allow for the use of a knee prosthesis having amobile bearing.

The components of a fixed-bearing knee prosthesis are typically providedby the manufacturer in matching sizes. Specifically, most currentlyavailable fixed-bearing knee prostheses allow the surgeon to use anumber of bearing sizes for a particular size of femoral component, buteach bearing size is generally matched to a particular size of tibialtray.

SUMMARY

According to one aspect, a fixed-bearing knee prosthesis includes afemoral component having a medial condyle surface and a lateral condylesurface. The prosthesis also includes a bearing having a medial bearingsurface configured to articulate with the medial condyle surface of thefemoral component, and a lateral bearing surface configured toarticulate with the lateral condyle surface of the femoral component. Atibial tray is secured to the bearing. The tibial tray has a platformwith an elongated stem extending downwardly from a lower surfacethereof. The platform has a posterior buttress extending along aposterior section of a perimeter of the platform and extending upwardlyfrom an upper surface of the platform. An anterior buttress extendsalong an anterior section of the perimeter of the platform and upwardlyfrom the upper surface of the platform. The tibial tray also has anelongated bore that opens into the upper surface of the posteriorbuttress.

The posterior buttress is generally Y-shaped and has a first armextending along a posterior edge of the platform and having a firstundercut defined therein. A second arm extends along the posterior edgeof the platform in a direction away from the first arm and has a secondundercut defined therein. A third arm extends anteriorly away from thefirst arm and the second arm.

A first imaginary line extends along a lateral-most edge of the firstarm, with a second imaginary line extending along a medial-most edge ofthe second arm and intersecting the first imaginary line to define anangle of intersection therebetween.

In some illustrative embodiments, the angle of intersection of theimaginary lines is between 45-145°. In some illustrative embodiments,the angle of intersection of the imaginary lines is between 60-120°. Ina specific illustrative embodiment, the angle of intersection of theimaginary lines is approximately 90°.

In some illustrative embodiments, the anterior buttress is generallyT-shaped. In such cases, the anterior buttress includes a first armextending along an anterior edge of the platform with a first undercutdefined therein, and a second arm extending along the anterior edge ofthe platform in a direction away from the first arm and with a secondundercut defined therein. A third arm extends posteriorly away from thefirst arm and the second arm.

The third arm of the posterior buttress may be contiguous with the thirdarm of the anterior buttress.

The bearing may include a first posterior tab positioned in the firstundercut defined in the first arm of the posterior buttress, a secondposterior tab positioned in the second undercut defined in the secondarm of the posterior buttress, a first anterior tab positioned in thefirst undercut defined in the first arm of the anterior buttress, and asecond anterior tab positioned in the second undercut defined in thesecond arm of the anterior buttress.

Both the medial bearing surface and the lateral bearing surface aredefined in the upper surface of the bearing. The lower surface of thebearing contacts the upper surface of the platform and includes aposterior recess and an anterior recess formed therein. The posteriorbuttress is positioned in the posterior recess and the anterior buttressis positioned in the anterior recess. The posterior recess may becontiguous with the anterior recess.

According to another aspect, a fixed-bearing knee prosthesis includes afemoral component having a medial condyle surface and a lateral condylesurface. The prosthesis also includes a bearing having a medial bearingsurface configured to articulate with the medial condyle surface of thefemoral component, and a lateral bearing surface configured toarticulate with the lateral condyle surface of the femoral component. Atibial tray is secured to the bearing. The tibial tray has a platformwith an elongated stem extending downwardly from a lower surfacethereof. The platform has a posterior buttress extending along aposterior section of a perimeter of the platform and extending upwardlyfrom an upper surface of the platform. An anterior buttress extendsalong an anterior section of the perimeter of the platform and upwardlyfrom the upper surface of the platform. The tibial tray also has anelongated bore that opens into the upper surface of the posteriorbuttress.

The posterior buttress is generally Y-shaped and has a first armextending along a posterior edge of the platform with a first undercutdefined therein, and a second arm extending along the posterior edge ofthe platform in a direction away from the first arm with a secondundercut defined therein. A third arm extends anteriorly away from thefirst arm and the second arm.

The anterior buttress includes a first arm extending along an anterioredge of the platform with a first undercut defined therein. A second armof the anterior buttress extends along the anterior edge of the platformin a direction away from the first arm of the anterior buttress with asecond undercut defined therein.

A first imaginary line extends along a posterior-most edge of the firstarm of the anterior buttress and a posterior-most edge of the second armof the anterior buttress. A second imaginary line extends along thelongitudinal axis of the third arm of the posterior buttress andintersects the first imaginary line to define an angle of intersectiontherebetween. The angle of intersection is approximately 90°.

The anterior buttress may include a third arm extending posteriorly awayfrom the first arm and the second arm in a direction parallel to thesecond imaginary line. The third arm of the posterior buttress may becontiguous with the third arm of the anterior buttress.

The bearing may include a first posterior tab positioned in the firstundercut defined in the first arm of the posterior buttress, a secondposterior tab positioned in the second undercut defined in the secondarm of the posterior buttress, a first anterior tab positioned in thefirst undercut defined in the first arm of the anterior buttress, and asecond anterior tab positioned in the second undercut defined in thesecond arm of the anterior buttress.

Both the medial bearing surface and the lateral bearing surface aredefined in the upper surface of the bearing. The lower surface of thebearing contacts the upper surface of the platform and includes aposterior recess and an anterior recess formed therein. The posteriorbuttress is positioned in the posterior recess and the anterior buttressis positioned in the anterior recess. The posterior recess may becontiguous with the anterior recess.

According to another aspect, a fixed-bearing knee prosthesis includes afemoral component having a medial condyle surface and a lateral condylesurface, and a tibial tray having a platform with an elongated stemextending downwardly from a lower surface thereof. The platform has agenerally Y-shaped posterior buttress extending upwardly from an uppersurface of the platform. A pair of arms of the posterior buttress extendalong a posterior section of a perimeter of the platform. Each of thepair of arms has an undercut defined therein. The platform also has ananterior buttress extending along an anterior section of the perimeterof the platform and extending upwardly from the upper surface of theplatform. The knee prosthesis also includes a plurality of bearingsconfigured to be secured to the tibial tray. Each of the plurality ofbearings has a width that is different from at least some of the otherof the plurality of bearings. Each of the plurality of bearings also hasan upper surface having a medial bearing surface configured toarticulate with the medial condyle surface of the femoral component anda lateral bearing surface configured to articulate with the lateralcondyle surface of the femoral component. A lower surface of each of theplurality of bearings has at least one recess defined therein to receivethe posterior buttress and the anterior buttress. Each of the pluralityof bearings also includes a pair of posterior tabs arranged to berespectively received in the undercuts defined in the pair of arms ofthe posterior buttress. The tibial tray also has an elongated bore thatopens into the upper surface of the posterior buttress.

The recess of the bearing may define a single, contiguous recess thatreceives both the posterior buttress and the anterior buttress.

The anterior buttress may be generally T-shaped with a pair of armsextending along an anterior edge of the platform. Each of the pair ofarms of the anterior buttress may have an undercut defined therein. Eachof the plurality of bearings may further include a pair of anterior tabsarranged to be respectively received in the undercuts defined in thepair of arms of the anterior buttress.

The posterior buttress may be contiguous with the anterior buttress.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description particularly refers to the following figures,in which:

FIG. 1 is an exploded perspective view of a fixed-bearing kneeprosthesis;

FIG. 2 is a bottom perspective view of the bearing of the kneeprosthesis of FIG. 1;

FIG. 3 is a perspective view of the tibial tray of the knee prosthesisof FIG. 1;

FIG. 4 is a plan view of the tibial tray of the knee prosthesis of FIG.1;

FIG. 5 is a diagrammatic plan view of a number of differently sizedtibial trays of the knee prosthesis of FIG. 1;

FIGS. 6-9 are similar to FIG. 4, but showing different embodiments ofthe tibial tray; and

FIGS. 10-14 are similar to FIGS. 1-5, respectively, but showing anotherembodiment of a fixed-bearing knee prosthesis.

DETAILED DESCRIPTION OF THE DRAWINGS

While the concepts of the present disclosure are susceptible to variousmodifications and alternative forms, specific exemplary embodimentsthereof have been shown by way of example in the drawings and willherein be described in detail. It should be understood, however, thatthere is no intent to limit the concepts of the present disclosure tothe particular forms disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

Terms representing anatomical references, such as anterior, posterior,medial, lateral, superior, inferior, etcetera, may be used throughoutthis disclosure in reference to both the orthopaedic implants describedherein and a patient's natural anatomy. Such terms have well-understoodmeanings in both the study of anatomy and the field of orthopaedics. Useof such anatomical reference terms in the specification and claims isintended to be consistent with their well-understood meanings unlessnoted otherwise.

Referring now to FIGS. 1-4, there is shown a fixed-bearing kneeprosthesis 10. The knee prosthesis 10 includes a femoral component 12, atibial tray 14, and a bearing 16. The tibial tray 14 includes a platform18 having a fixation member, such as an elongated stem 20, extendingaway from its lower surface 22. The elongated tibial stem 20 isconfigured to be implanted into a surgically prepared end of a patient'stibia (not shown). It should be appreciated that other fixation members,such as one or more short pegs or posts, may be used in lieu of theelongated stem 20. The bearing 16 is securable to the tibial tray 14. Inparticular, as will be discussed below in greater detail, the bearing 16may be snap-fit to the tibial tray 14. In such a way, the bearing 16 isfixed relative to the tibial tray 14 (i.e., it is not rotatable ormoveable in the anterior/posterior or medial/lateral directions).

The bearing 16 includes a lateral bearing surface 26 and a medialbearing surface 28. The bearing surfaces 26, 28 are configured toarticulate with a lateral condyle surface 30 and a medial condylesurface 32, respectively, of the femoral component 12. Specifically, thefemoral component 12 is configured to be implanted into a surgicallyprepared end of the patient's femur (not shown), and is configured toemulate the configuration of the patient's natural femoral condyles. Assuch, the lateral condyle surface 30 and the medial condyle surface 32are configured (e.g., curved) in a manner which mimics the condyles ofthe natural femur. The lateral condyle surface 30 and the medial condylesurface 32 are spaced apart from one another thereby defining anintercondylar notch therebetween.

The components of the knee prosthesis 10 that engage the natural bone,such as the femoral component 12 and the tibial tray 14, may beconstructed with a biocompatible metal, such as a cobalt chrome alloy,although other materials may also be used. The bone engaging surfaces ofthese components may be textured to facilitate cementing the componentto the bone. Such surfaces may also be porous coated to promote boneingrowth for permanent fixation.

The bearing 16 may be constructed with a material that allows for smootharticulation between the bearing 16 and the femoral component 12, suchas a polymeric material. One such polymeric material is polyethylenesuch as ultrahigh molecular weight polyethylene (UHMWPE).

As shown in FIG. 2, the lower surface 36 of the bearing 16 includes alateral pedestal 34 and a medial pedestal 38. The pedestals 34, 38 havea number of posterior tabs 40 defined therein. A number of anterior tabs42 are also defined in the bearing 16.

As shown in FIGS. 3 and 4, a generally Y-shaped posterior buttress 44extends upwardly from the upper surface 24 of the tibial tray 14. In theillustrative embodiment described herein, the posterior buttress 44 hasa pair of arms 46, 48 extending along a posterior section of theperimeter of tibial tray's platform 18. Specifically, the lateral arm 46of the posterior buttress 44 extends along the posterior edge 50 on thelateral side of the platform 18, whereas the medial arm 48 of theposterior buttress 44 extends along the posterior edge 50 on the medialside of the platform 18 in a direction away from the lateral arm 46. Athird arm 52 of the posterior buttress 44 extends anteriorly away fromthe intersection of the lateral arm 46 and the medial arm 48 (i.e., in adirection toward the center of the platform 18).

The posterior buttress 44 has a pair of undercuts 54, 56 definedtherein. Specifically, the lateral undercut 54 is defined in the lateralarm 46 of the posterior buttress 44, with the medial undercut 56 beingdefined in the medial arm 48 of the posterior buttress 44.

As can be seen in FIGS. 1, 3-10, and 12-14, the tibial tray 14 has anelongated bore 58 formed therein. A superior end 60 of the elongatedbore 58 opens into the upper surface 62 of the posterior buttress 44. Inthe illustrative embodiments shown in FIGS. 9, 10, and 12-14, thesuperior end 60 of the elongated bore 58 opens into the third arm 52 ofthe posterior buttress 44. More particularly, in such illustrativeembodiments, the superior end 60 of the elongated bore 58 opens into theanterior end of the third arm 52 of the posterior buttress 44. This isshown geometrically in FIGS. 9 and 13 in which an imaginary line 114extending in the medial/lateral direction bisects the third arm 52 intoan anterior half 116 and a posterior half 118. The superior end 60 ofthe elongated bore 58 opens into the anterior end of the third arm 52 ofthe posterior buttress 44 at a location in its anterior half 116.

As can be seen best in FIG. 12, the elongated bore 58 extends in thesuperior/inferior direction. As a result, the elongated bore 58 extendsaway from its superior end 60 in the direction toward the distal end 120of the tibial tray's elongated stem 20.

As also shown in FIGS. 3 and 4, a generally T-shaped anterior buttress64 extends upwardly from the upper surface 24 of the tibial tray 14. Inthe illustrative embodiment described herein, the anterior buttress 64has a pair of arms 66, 68 extending along an anterior section of theperimeter of tibial tray's platform 18. Specifically, the lateral arm 66of the anterior buttress 64 extends along the anterior edge 70 on thelateral side of the platform 18, whereas the medial arm 68 of theanterior buttress 64 extends along the anterior edge 70 on the medialside of the platform 18 in a direction away from the lateral arm 66. Athird arm 72 of the anterior buttress 64 extends posteriorly away fromthe intersection of the lateral arm 66 and the medial arm 68 (i.e., in adirection toward the center of the platform 18).

The anterior buttress 64 has a pair of undercuts 74, 76 defined therein.Specifically, the lateral undercut 74 is defined in the lateral arm 66of the anterior buttress 64, with the medial undercut 76 being definedin the medial arm 68 of the anterior buttress 64.

In the illustrative embodiment of FIGS. 1-4, the posterior buttress 44of the tibial tray 14 is contiguous with the tray's anterior buttress64. Specifically, as shown in FIG. 4, the third arm 52 of the posteriorbuttress 44 is contiguous with the third arm 72 of the anterior buttress64. However, as will be discussed below in greater detail, otherembodiments are contemplated, including arrangements in which thebuttresses are not contiguous. Moreover, the two buttresses 44, 64 areherein described as being of a similar height, although the buttressescould be embodied has having dissimilar heights.

To secure the tibial bearing 16 to the tibial tray 14, the posteriortabs 40 of the bearing 16 are positioned in the posterior undercuts 54,56 of the tibial tray 14. Thereafter, the anterior portion of the tibialbearing 16 is advanced downwardly toward the tibial tray 14 such thatthe anterior tabs 42 of the tibial bearing 16 are deflected by theanterior buttress 64 and thereafter snapped into the anterior undercuts74, 76 of the anterior buttress thereby securing the bearing 16 to thetray 14.

As the anterior portion of the bearing 16 is advanced downwardly in sucha manner, the buttresses 44, 64 of the tibial tray 14 are capturedbetween the pedestals 34, 38 of the bearing's lower surface 36.Specifically, the lower surface 36 of the bearing 16 has a posteriorrecess 78 and an anterior recess 80 defined therein. The posteriorrecess 78 is configured to compliment the shape of the posteriorbuttress 44 of the tibial tray 14. That is, when the bearing 16 issecured to the tibial tray 14, the sidewalls of the pedestals 34, 38which define the posterior recess 78 contact the edges of the posteriorbuttress 44. Likewise, the anterior recess 80 is configured tocompliment the shape of the anterior buttress 64 of the tibial tray14—i.e., when the bearing 16 is secured to the tibial tray 14, thesidewalls of the pedestals 34, 38 which define the anterior recess 80contact the edges of the anterior buttress 64. The dimensions of therecesses 78, 80 and the buttresses 44, 64 are selected such that arelatively tight fit is achieved. In such a way, the bearing 16 is fixedrelative to the tibial tray 14. In particular, the configuration of thebuttresses 44, 46 and the pedestals 34, 38 formed in the lower surface36 of the bearing 16 prevent movement of the bearing 16 relative thetibial tray 14 in the anterior/posterior direction and themedial/lateral direction. Moreover, the posterior tabs positioned in theundercuts 54, 56 and the anterior tabs 42 positioned in the undercuts74, 76 prevent lift off of the bearing 16 from the tibial tray 14.Rotational micromotion is reduced, if not prevented all together, by therelatively tight fit of the buttresses 44, 64 of the tibial tray 14 intothe recesses 78, 80 of the bearing 16—particularly along the third arm52 of the posterior buttress 44 and/or the third arm 72 of the anteriorbuttress 64.

As alluded to above, in the illustrative embodiment described herein,the posterior buttress 44 is embodied as a generally Y-shaped structurehaving a pair of arms 46, 48 extending in opposite directions along theposterior edge 50 of the tray's platform 18, with a third arm 52extending anteriorly from the posterior edge 50 of the tibial tray 14(i.e., in a direction toward the center of the tray's platform 18). Asshown in FIG. 4, the lateral arm 46 of the posterior buttress 44includes a lateral-most edge 86, whereas the medial arm 48 of theposterior buttress 44 has a medial-most edge 88. An imaginary line 82extends along the lateral-most edge 86 and intersects an imaginary line84 that extends along the medial-most edge 88 to define an angle ofintersection (α). In the exemplary embodiments described herein, theangle of intersection (α) is between 45-145°. In more specificillustrative embodiments, the angle of intersection (α) is between60-120°. In one such specific illustrative embodiment, the angle ofintersection (α) is approximately 90°. Examples of such illustrativeembodiments of the posterior buttress 44 are shown in FIGS. 6-9.

It should be appreciated that increasing the angle of intersection (α)reduces micromotion, while decreasing the angle of intersection (α)increases the load bearing surface area of the tibial tray 14. Althoughother configurations may be utilized, it has been found that arrangingthe arms 46, 48 of the posterior buttress 44 as described above (i.e.,having an angle of intersection (α) between 60-120°) provides anunexpectedly beneficial working balance between these twoconsiderations. On particularly well-balanced arrangement of theposterior buttress 44 is found in the illustrative embodiment where theangle of intersection (α) is approximately 90°.

As alluded to above, in the illustrative embodiment described herein,the anterior buttress 64 is embodied as a generally T-shaped structurehaving a pair of arms 66, 68 extending in opposite directions along theanterior edge 70 of the tray's platform 18, with a third arm 64extending posteriorly from the anterior edge 70 of the tibial tray 14(i.e., in a direction toward the center of the tray's platform 18). Asshown in FIG. 4, the lateral arm 66 of the anterior buttress 64 includesa posterior-most edge 90, whereas the medial arm 68 of the anteriorbuttress 64 has a posterior-most edge 92. An imaginary line 94 extendsalong both the posterior-most edge 90 of the lateral arm 66 and theposterior-most edge 92 of the medial arm 68. An imaginary center line 96extends along a longitudinal axis of the third arm 52 of the posteriorbuttress 44. As shown in FIG. 4, the imaginary center line 96 bisectsthe third arm 52 of the posterior buttress 44. The imaginary line 94extending along the posterior-most edges 90, 92 of the arms 66, 68 ofthe anterior buttress 64 intersects the imaginary center line 96extending along the longitudinal axis of the third arm 52 of theposterior buttress 44 to define an angle of intersection (β). In theillustrative embodiments described herein, the arms 66, 68 (and hencethe undercuts 74, 76) of the anterior buttress 64 are configured toextend in the medial/lateral direction. As a result, in the illustrativeembodiments described herein, the angle of intersection (β) isapproximately 90°. As shown in FIGS. 6-9, such is the case throughoutnumerous illustrative embodiments of the anterior buttress 64.

A given design of a fixed-bearing knee prosthesis is typically madecommercially available in a variety of different sizes, particularly ina variety of different widths. This is done to accommodate the manyvariations in patient size and anatomy across a population. However, theconfiguration of the fixed-knee prosthesis 10 of the present disclosureallows for a high degree of flexibility in regard to the sizing of thetibial tray 14 and the bearing 16. In particular, FIG. 5 is adiagrammatic representation of a plurality of differently-sized tibialtrays 14 superimposed upon one another. As can be seen, despite each ofthe individual trays 14 having a size (e.g., width) that is differentfrom the other trays 14 of the group, the basic configuration of theposterior buttress 44 and the anterior buttress 64 remains the sameacross the range of differently-sized trays 14. Specifically, thelocation of the undercuts 54, 56 defined in posterior buttress 44,respectively, remains the same across the range of differently-sizedtrays 14. Even though the posterior undercuts 54, 56 remain in the samelocation across the range of differently-sized trays 14, the width ofthe arms 46, 48 is varied to accommodate the overall width of a giventray 14. In a similar manner, the location of the undercuts 74, 76defined in anterior buttress 64, respectively, remains the same acrossthe range of differently-sized trays 14, although the width of the arms66, 68 is varied to accommodate the overall width of a given tray 14. Asshown in FIG. 5, the size and configuration of the third arms 52, 72 ofthe posterior buttress 44 and the anterior buttress 64, respectively,remain unchanged across the range of differently-sized trays 14.

Differently-sized bearings 16 may also be configured in such a manner.In particular, a plurality of the bearings 16 may be designed with eachof such a plurality of bearings 16 having a different size, particularlya different width. However, each of such differently-sized bearings 16may include mating features that are commonly-sized and commonly-locatedwith the commonly-sized and commonly-located features of the tibial tray14 described above. In particular, each of the bearings 16 across arange of differently-sized bearings 16 may include a posterior recess 78and an anterior recess 80 that is positioned and sized to tightly fitagainst the edges of the posterior buttress 44 and the anterior buttress64, respectively, of each of the tibial trays 14 across the range ofdifferently-sized trays 14.

The posterior tabs 40 are commonly-sized and commonly-located across therange of differently-sized bearings 16 so that they are positioned inthe respective posterior undercuts 54, 56 of each of the tibial trays 14across the range of differently-sized trays 14. Likewise, the anteriortabs 42 are commonly-sized and commonly-located across the range ofdifferently-sized bearings 16 so that they are positioned in therespective anterior undercuts 74, 76 of each of the tibial trays 14across the range of differently-sized trays 14.

It should be appreciated from the above-discussion that the generalconfiguration of the buttresses 44, 64 (including contiguous variationsthereof) is the same across the range of differently-sized tibial trays14. Likewise, the general configuration of the recesses 78, 80(including contiguous variations thereof) and the general configurationof tabs 40, 42 are the same across the range of differently-sizedbearings 16. As such, any size bearing 16 may be secured to any sizetibial tray 14. This provides the orthopaedic surgeon with greaterflexibility of matching the knee prosthesis 10 to a particular patient'sanatomy.

As shown in FIGS. 6-9, other configurations of the posterior buttress 44and the anterior buttress 64 are also contemplated. For example, in theillustrative embodiment of FIG. 6, the third arm 52 of the posteriorbuttress 44 and the third arm 72 of the anterior buttress 64 areconfigured to define a contiguous structure having a substantiallyconstant width throughout its entire length. It should be appreciatedthat the recesses 78, 80 defined in the lower surface 36 of the bearing16 are likewise reshaped in the embodiment of FIG. 6 to accommodate thedifferent shape of the buttresses 44, 64 of the tibial tray 14. In otherwords, while it's contemplated that the design of the buttresses 44, 64may be altered, it is also contemplated that the design of the recesses78, 80 is altered accordingly to compliment the configuration of thebuttresses 44, 64. It is also contemplated that the generalconfiguration of the buttresses 44, 64 of FIG. 6, along with thecorresponding configuration of the recesses 78, 80 and tabs 40, 42 ofthe complimentary bearing 16, may also remain the same across a range ofdifferently-sized trays 14 and bearings 16 to accommodate theinterchangeability of various sizes of trays and bearings in a similarmanner to as described above in regard to FIG. 5.

As shown in the illustrative embodiment of FIG. 7, the third arm 52 ofthe posterior buttress 44 is not contiguous with the third arm 72 of theanterior buttress 64. In other words, there is a gap between the arms52, 72. It should be appreciated that the recesses 78, 80 defined in thelower surface 36 of the bearing 16 are likewise reshaped in theembodiment of FIG. 7 to accommodate the different shape of thebuttresses 44, 64 of the tibial tray 14. In other words, the design ofthe recesses 78, 80 is altered to compliment the configuration of theseparated buttresses 44, 64. It is also contemplated that the generalconfiguration of the separated buttresses 44, 64 of FIG. 7, along withthe corresponding configuration of the recesses 78, 80 and tabs 40, 42of the complimentary bearing 16, may also remain the same across a rangeof differently-sized trays 14 and bearings 16 to accommodate theinterchangeability of various sizes of trays and bearings in a similarmanner to as described above in regard to FIG. 5.

Turning to the embodiment of FIG. 8, the anterior buttress 64 isconfigured without the third arm 72. Moreover, the lateral arm 66 of theanterior buttress is spaced apart from the medial arm 68—i.e., there isa gap between the arms 66, 68. It should be appreciated that therecesses 78, 80 defined in the lower surface 36 of the bearing 16 arelikewise reshaped in the embodiment of FIG. 8 to accommodate thedifferent shape of the buttresses 44, 64 of the tibial tray 14. In otherwords, the design of the recesses 78, 80 is altered to compliment theconfiguration of the buttresses 44, 64. It is also contemplated that thegeneral configuration of the buttresses 44, 64 of FIG. 8, along with thecorresponding configuration of the recesses 78, 80 and tabs 40, 42 ofthe complimentary bearing 16, may also remain the same across a range ofdifferently-sized trays 14 and bearings 16 to accommodate theinterchangeability of various sizes of trays and bearings in a similarmanner to as described above in regard to FIG. 5.

Yet another embodiment of the knee prosthesis 10 is shown in FIG. 9.Like the embodiment of FIG. 8, the anterior buttress 64 is configuredwithout the third arm 72. However, unlike the design of FIG. 8, thelateral arm 66 of the anterior buttress is not spaced apart from themedial arm 68, but rather is contiguous therewith. Moreover, the thirdarm 52 of the posterior buttress 44 is longer than that of theembodiment shown in FIG. 8. As with the other embodiments describedherein, it should be appreciated that the recesses 78, 80 defined in thelower surface 36 of the bearing 16 are likewise reshaped in theembodiment of FIG. 9 to accommodate the different shape of thebuttresses 44, 64 of the tibial tray 14. In other words, the design ofthe recesses 78, 80 is altered to compliment the configuration of thebuttresses 44, 64. It is also contemplated that the generalconfiguration of the buttresses 44, 64 of FIG. 9, along with thecorresponding configuration of the recesses 78, 80 and tabs 40, 42 ofthe complimentary bearing 16, may also remain the same across a range ofdifferently-sized trays 14 and bearings 16 to accommodate theinterchangeability of various sizes of trays and bearings in a similarmanner to as described above in regard to FIG. 5.

A further embodiment of the knee prosthesis 10 is shown in FIGS. 10-14.Like the embodiment of FIGS. 8 and 9, the anterior buttress 64 isconfigured without the third arm 72. Like the design of FIG. 9, thelateral arm 66 of the anterior buttress 64 is contiguous with the medialarm 68 of the anterior buttress 64. Specifically, as shown in FIG. 13,the anterior buttress 64 defines a continuous, monolithic structure inwhich proximal ends of the lateral and medial arms 66, 68 are conjoined(i.e., spatially secured to one another) at location on the anterioredge 70 at the anterior-most point 98 of the tray's platform 18. Thelateral arm 66 extends laterally away from the anterior-most point 98 ofthe tray's platform and terminates at its lateral end 100 located at apoint 102 on the anterior edge 70 of the platform 18 between theanterior-most point 98 of the tray's platform and the lateral-most point104 of the tray's platform. The medial arm 68 extends medially away fromthe anterior-most point 98 of the tray's platform and terminates at itsmedial end 106 located at a point 108 on the anterior edge 70 of theplatform 18 between the anterior-most point 98 of the tray's platformand the medial-most point 110 of the tray's platform.

Unlike the design of FIG. 9, the posterior-most edge of the anteriorbuttress 64 of the design of FIGS. 10-14 is curved (i.e.,arcuate-shaped). In particular, as shown most clearly in FIG. 13, theimaginary line 94 extending along the posterior-most edge 90 of thelateral arm 66 and the posterior-most edge 92 of the medial arm 68 iscurved along a constant radius. It should be appreciated that since thearms 66, 68 of the anterior buttress 64 are contiguous, theposterior-most edge 90 of the lateral arm 66 and the posterior-most edge92 of the medial arm 68 define a single, continuous, uninterrupted edge.

Moreover, the anterior buttress 64 of the design of the knee prosthesis10 shown in FIGS. 10-14 includes a single anterior undercut 74 (i.e.,the second undercut 76 has been omitted). The anterior undercut 74 iscentered on the intersection of the two arms 66, 68 defining theanterior buttress 64. In other words, the imaginary line 94 extendingalong the posterior-most edge 90 of the lateral arm 66 and theposterior-most edge 92 of the medial arm 68 has a midpoint 112. Theanterior undercut 74 is centered on the midpoint 112. It should beappreciated that the lower surface 36 of the bearing 16 includes asingle anterior tab 42 sized and positioned to be received into thesingle anterior undercut 74 (see FIG. 11).

Like the designs of FIGS. 7-9, the anterior buttress 64 of the kneeprosthesis 10 shown in FIGS. 10-14 is discontiguous with the posteriorbuttress 44. In other words, the buttresses 44, 64 are spaced apart fromone another such that there is a gap therebetween. As with the otherembodiments described herein, it should be appreciated that the recesses78, 80 defined in the lower surface 36 of the bearing 16 are likewisereshaped in the embodiment of FIGS. 10-14 (relative to the embodimentsof FIGS. 1-9) to accommodate the different shape of the buttresses 44,64 of the tibial tray 14. In other words, as shown in FIG. 11, thedesign of the recesses 78, 80 is altered to compliment the configurationof the buttresses 44, 64.

Moreover, as shown in FIG. 14, the general configuration of thebuttresses 44, 64 of FIGS. 10-13, along with the correspondingconfiguration of the recesses 78, 80 and tabs 40, 42 of thecomplimentary bearing 16, remain the same across a range ofdifferently-sized trays 14 and bearings 16 to accommodate theinterchangeability of various sizes of trays and bearings in a similarmanner to as described above in regard to FIG. 5.

As described herein, the various designs of the knee prosthesis 10 allowfor the enhanced interchangeability of differently-sized components. Inparticular, any one of a plurality of differently-sized bearings may besecured to any one of a plurality of differently-sized tibial trays. Asa result, articulation surface geometries and other features of thebearing may be enhanced for each size of femoral component. Suchinterchangeability also allows for smaller size increments in the designof a range of femoral components.

While the disclosure has been illustrated and described in detail in thedrawings and foregoing description, such an illustration and descriptionis to be considered as exemplary and not restrictive in character, itbeing understood that only illustrative embodiments have been shown anddescribed and that all changes and modifications that come within thespirit of the disclosure are desired to be protected.

There are a plurality of advantages of the present disclosure arisingfrom the various features of the apparatus, system, and method describedherein. It will be noted that alternative embodiments of the apparatus,system, and method of the present disclosure may not include all of thefeatures described yet still benefit from at least some of theadvantages of such features. Those of ordinary skill in the art mayreadily devise their own implementations of the apparatus, system, andmethod that incorporate one or more of the features of the presentinvention and fall within the spirit and scope of the present disclosureas defined by the appended claims.

The invention claimed is:
 1. A fixed-bearing knee prosthesis,comprising: a femoral component having a medial condyle surface and alateral condyle surface, a bearing having (i) a medial bearing surfaceconfigured to articulate with the medial condyle surface of the femoralcomponent, and (ii) a lateral bearing surface configured to articulatewith the lateral condyle surface of the femoral component, and a tibialtray secured to the bearing, the tibial tray having a platform with afixation member extending downwardly from a lower surface thereof, theplatform having (i) a posterior buttress extending along a posteriorsection of a perimeter of the platform and extending upwardly from anupper surface of the platform, (ii) an anterior buttress extending alongan anterior section of the perimeter of the platform and extendingupwardly from the upper surface of the platform, and (iii) an elongatedbore having a superior end that opens into an upper surface of theposterior buttress, wherein the anterior buttress has (i) a first armextending along an anterior edge of the platform, (ii) a second armextending along the anterior edge of the platform in a direction awayfrom the first arm of the anterior buttress, the second arm beingcontiguous with the first arm, and (iii) an undercut defined therein,wherein the posterior buttress is generally Y-shaped and has (i) a firstarm extending along a posterior edge of the platform and having a firstundercut defined therein, (ii) a second arm extending along theposterior edge of the platform in a direction away from the first armand having a second undercut defined therein, and (iii) a third armextending anteriorly away from the first arm and the second arm, andwherein (i) a first imaginary line extends along a lateral-most edge ofthe first arm of the posterior buttress, (ii) a second imaginary lineextends along a medial-most edge of the second arm of the posteriorbuttress and intersects the first imaginary line to define an angle ofintersection therebetween, and (iii) the angle of intersection isbetween 45-145°.
 2. The knee prosthesis of claim 1, wherein the angle ofintersection is approximately 60-120°.
 3. The knee prosthesis of claim1, wherein the angle of intersection is approximately 90°.
 4. The kneeprosthesis of claim 1, wherein the superior end of the elongated boreopens into the third arm of the posterior buttress.
 5. The kneeprosthesis of claim 1, wherein: the fixation member of the tibial traycomprises an elongated stem extending downwardly from the lower surfaceof the platform, and the elongated bore extends away from the uppersurface of the posterior buttress in the direction toward a distal endof the stem.
 6. The knee prosthesis of claim 1, wherein the elongatedbore of the tibial tray extends in the superior/inferior direction. 7.The knee prosthesis of claim 1, wherein: a third imaginary line extendsin a medial/lateral direction and bisects the third arm of the posteriorbuttress so as to divide the third arm of the posterior buttress into ananterior half and a posterior half, and the superior end of theelongated bore of the tibial tray opens into the upper surface of theposterior buttress at a location in the anterior half of the third armof the posterior buttress.
 8. The knee prosthesis of claim 1, wherein:the bearing has an upper surface and a lower surface, both the medialbearing surface and the lateral bearing surface are defined in the uppersurface of the bearing, the lower surface of the bearing contacts theupper surface of the platform, the lower surface of the platform has aposterior recess and an anterior recess formed therein, and theposterior buttress is positioned in the posterior recess and theanterior buttress is positioned in the anterior recess.
 9. The kneeprosthesis of claim 8, wherein the posterior buttress is discontiguouswith the anterior buttress.
 10. A fixed-bearing knee prosthesis,comprising: a femoral component having a medial condyle surface and alateral condyle surface, a bearing having (i) a medial bearing surfaceconfigured to articulate with the medial condyle surface of the femoralcomponent, and (ii) a lateral bearing surface configured to articulatewith the lateral condyle surface of the femoral component, and a tibialtray secured to the bearing, the tibial tray having a platform with afixation member extending downwardly from a lower surface thereof, theplatform having (i) a posterior buttress extending along a posteriorsection of a perimeter of the platform and extending upwardly from anupper surface of the platform, (ii) an anterior buttress extending alongan anterior section of the perimeter of the platform and extendingupwardly from the upper surface of the platform, and (iii) an elongatedbore having a superior end that opens into an upper surface of theposterior buttress, wherein the posterior buttress is generally Y-shapedand has (i) a first arm extending along a posterior edge of the platformand having a first undercut defined therein, (ii) a second arm extendingalong the posterior edge of the platform in a direction away from thefirst arm and having a second undercut defined therein, and (iii) athird arm extending anteriorly away from the first arm and the secondarm, wherein the anterior buttress has (i) a first arm extending alongan anterior edge of the platform, (ii) a second arm extending along theanterior edge of the platform in a direction away from the first arm ofthe anterior buttress, and (iii) an undercut defined therein, andwherein (i) an imaginary line extends along a posterior-most edge of thefirst arm of the anterior buttress and a posterior-most edge of thesecond arm of the anterior buttress, and (ii) the imaginary line definesa curve having a constant radius.
 11. The knee prosthesis of claim 10,wherein the superior end of the elongated bore opens into the third armof the posterior buttress.
 12. The knee prosthesis of claim 10, wherein:the fixation member of the tibial tray comprises an elongated stemextending downwardly from the lower surface of the platform, and theelongated bore extends away from the upper surface of the posteriorbuttress in the direction toward a distal end of the stem.
 13. The kneeprosthesis of claim 10, wherein the elongated bore of the tibial trayextends in the superior/inferior direction.
 14. The knee prosthesis ofclaim 10, wherein: a third imaginary line extends in a medial/lateraldirection and bisects the third arm of the posterior buttress so as todivide the third arm of the posterior buttress into an anterior half anda posterior half, and the superior end of the elongated bore of thetibial tray opens into the upper surface of the posterior buttress at alocation in the anterior half of the third arm of the posteriorbuttress.
 15. The knee prosthesis of claim 10, wherein: the bearing hasan upper surface and a lower surface, both the medial bearing surfaceand the lateral bearing surface are defined in the upper surface of thebearing, the lower surface of the bearing contacts the upper surface ofthe platform, the lower surface of the platform has a posterior recessand an anterior recess formed therein, and the posterior buttress ispositioned in the posterior recess and the anterior buttress ispositioned in the anterior recess.
 16. The knee prosthesis of claim 10,wherein the posterior buttress is discontiguous with the anteriorbuttress.
 17. A fixed-bearing knee prosthesis, comprising: a femoralcomponent having a medial condyle surface and a lateral condyle surface,a tibial tray having a platform with a fixation member extendingdownwardly from a lower surface thereof, the platform having (i) agenerally Y-shaped posterior buttress extending upwardly from an uppersurface of the platform and having a pair of arms extending along aposterior section of a perimeter of the platform, each of the pair ofarms having an undercut defined therein, and (ii) an anterior buttressextending along an anterior section of the perimeter of the platform andextending upwardly from the upper surface of the platform, the anteriorbuttress being discontiguous with the posterior buttress and having anundercut defined therein, and (iii) an elongated bore having a superiorend that opens into an upper surface of the posterior buttress, and aplurality of bearings configured to be separately secured to the tibialtray, wherein each of the plurality of bearings has (i) a width that isdifferent from at least some of the other of the plurality of bearings,(ii) an upper surface having a medial bearing surface configured toarticulate with the medial condyle surface of the femoral component anda lateral bearing surface configured to articulate with the lateralcondyle surface of the femoral component, (iii) a lower surface having aposterior recess defined therein to receive the posterior buttress andan anterior recess defined therein to receive the anterior buttress,(iv) a pair of posterior locking tabs arranged to be respectivelyreceived in the undercuts defined in each of the pair of arms of theposterior buttress, and (v) an anterior locking tab arranged to bereceived in the undercut defined in the anterior buttress.
 18. The kneeprosthesis of claim 17, wherein: the fixation member of the tibial traycomprises an elongated stem extending downwardly from the lower surfaceof the platform, and the elongated bore extends away from the uppersurface of the posterior buttress in the direction toward a distal endof the stem.
 19. The knee prosthesis of claim 17, wherein the elongatedbore of the tibial tray extends in the superior/inferior direction.